The present invention is directed to semiconductor devices and, more particularly, to packaged semiconductor devices having one or more semiconductor dies on a substrate with a cap.
Semiconductor device packaging fulfils basic functions such as providing electric connections and protecting the die against mechanical and environmental stresses. The completed semiconductor device may be mounted on a support with electrical connectors, such as a printed circuit board (PCB), for example. The semiconductor device has exposed external electrical contact surfaces or leads for connection to the electrical connectors on the support. Using surface mount technology, external electrical contact surfaces or leads of the package can be soldered directly to corresponding pads on the support, providing mechanical attachment as well as electrical connections.
Semiconductor devices are commonly packaged for surface mounting by encapsulating one or more semiconductor dies, the encapsulation process including embedding the die or dies in a molding compound. Various techniques are available for connecting the external electrical contact surfaces or leads of the package internally with electrical contact pads on the embedded semiconductor die. It is common to facilitate manufacturing operations by performing many of the operations on arrays of the components of the devices which are linked together, the links being severed during singulation of the devices.
In a metal base package, the substrate is an electrically and thermally conductive metal flag, which assists in dissipating heat. A metal flag structure may be provided, which has an array of the flags linked by frame members which are cut off and discarded during singulation. The flag structure may also include sets of electrical contact surfaces or leads which are supported by and integral with the frame members, until the devices are encapsulated and the frame members are cut off and discarded during singulation to isolate the electrical contact surfaces or leads from each other. This technique is limited to devices where the sets of electrical contacts are disposed at the periphery of the metal flag and the semiconductor die, on opposing sides or around all four sides.
In a laminate or ceramic base package, the substrate is an electrically insulating substrate bearing the external electrical contact surfaces. Examples of laminate base packages include ball grid array (BGA), pin grid array (PGA) and land grid array (LGA) packages. The electrically insulating materials used for such substrates are typically thermally insulating also, and hence do not assist in cooling the device.
A semiconductor device may have a cap that covers a face of the semiconductor die or dies. Such a cap may be formed of a thermally conductive material and function as a heat sink, distributing internally generated heat over the face of the semiconductor die or dies and dissipating the heat, by conduction radiation and/or convection, for example. Such a cap may be formed of an electrically conductive material and also function as an electromagnetic shield, typically in conjunction with an electrically conductive substrate beneath the semiconductor die or dies, in order to reduce electromagnetic interference effects.
Whether or not the substrate on which the die is mounted has similar properties to the cap, such a cap is particularly effective when the active face of the die is upwards and near to the cap. However, integrating the cap in the semiconductor device may involve extra process steps, increasing the cost of the device and introducing additional risks of manufacturing defects, which it is desirable to minimize or eliminate.